Another idle issue! Help! Options

[yrret7]

My idle is way to high. I've looked for a vaccum leak without success. The idle screw on the Ecu does not make any difference. The idle screw on the throttle body is turned all the way down. If i plug in the temp sensor the idle bounces and just about stalls . The aux air valve is working correctly and closes off. I'm running it now with the temp sensor in the manifold unpluged and the idle is at 2000 and won't go down. I tried pinching each vaccum hose with vise grips to find a leak. what i did find was that when I clamped the decal valve end port or side port hose the idle went down to 1000 rpm idle with no bounce. I clamped both ends of the vaccum hose from the manifold to the decal valve to make sure it as not leaking. no change. I have installed all new vaccum hoses with kit from AA.

Putting suction on the control port opens the decal valve and allows air to be blown through . So i guess that it works.

Why does closing the air flow to the decal valve by clamping the hose closed give me correct idle ???

Why does pluging in the air temp sensor cause the idle to bounce an stall if I don't feather the gas pedal?

Any thoughts??
I drove the car with the decal valve hose pinched closed and the car runs perfect!!

[r_towle]

Why does closing the air flow to the decal valve by clamping the hose closed give me correct idle ???

the hoses may not be hooked up correctly.

Why does pluging in the air temp sensor cause the idle to bounce an stall if I don't feather the gas pedal?

If you are talking about the ambient air temp sensor, it controls the cold start injector. If by plugging it in, you are adding more fuel, you may be flooding the motor and feathering the pedal will add more air to keep it running.

Rich

[pilothyer]

Incorrect hose orientation at the decell valve will cause high idle. Make sure the large hose from the intake manifold is connected to the large "end" port on the decell valve, and the large hose from the air filter box is connected to the large "side" port on the decell valve. and lastly the control or small "end" of the decell valve is connected to the intake manifold. Also if the decell valve is stuck open or the diaphram is leaking you can (for test purposes) disconnect it from the system. Disconnect the source vacuum to the decell valve by disconnecting the small hose running from the intake manifold to the small end of the decell valve. (Disconnect the small hose from the valve and plug the hose) Then disconnect the large hose comming from the intake manifold and plug it.

[pilothyer]

You said you drove the car with the decell valve pinched closed and the car runns perfect !!

This proves that the decell valve is either stuck open, plumbed incorrectly, or out of adjustment (set too low which makes it open at idle vacuum) Check the hose connections and try again, then come back to see if we can adjust the decell valve to operate at a higher vacuum (open under decelleration only)

[yrret7]

You said you drove the car with the decell valve pinched closed and the car runns perfect !!

This proves that the decell valve is either stuck open, plumbed incorrectly, or out of adjustment (set too low which makes it open at idle vacuum) Check the hose connections and try again, then come back to see if we can adjust the decell valve to operate at a higher vacuum (open under decelleration only)

The valve was out of adjustment and open at idle. I have adjusted is so that it is now closed at idle and I belive that it is working correctly. The idle is now steady at 1200.
I have still yet to figure out why when the air temp sensor is connected it causes the idle to bounce and stall.
Thanks for your help!!!
Terry

[pilothyer]

Terry...It is a common practice to disconnect the intake air temp sensor to fool the computor into an richer running condition (this will mask other problems) Your open decell valve caused a lean running system and that compensated for it. You need to reconnect the temp sensor, and then isolate the problem to other vacuum leaks....start with the diaphram on the distributor vacuum advance....remove the hose and plug it (the hose going to the intake) Then check your ignition timing, make sure your aux air valve is closing after warm up. (if not remove the hose that goes to it from the air cleaner and plug the hose. Try all this first and get back here for further instruction. Either way come back to let us know what you find. We will get to the bottom of this, and your easy starting, 950 RPM smooth running idle, quick accelerating Porsche will be back.............